1. Field of the Invention
The present invention relates to an encoder for encoding video data in a facsimile system or an image file and, more particularly, to an encoding apparatus for encoding video data input from a scanner or the like and to a decoding apparatus for decoding the video data encoded by the encoding apparatus.
2. Description of the Prior Art
As an encoding method of video data, an MH code, an MR code, an MMR code and the like according to CCITT recommendations are used for a facsimile system. In this case, a public telephone network is employed as a transmission line, and a maximum transmission rate is about 9,600 bps. Therefore, conversion of video data into the above-mentioned codes or vice versa can be performed by software processing. In recent years, a digital line network is becoming popular in various countries, and a transmission rate thereof is, e.g., 48 kbps, 64 kbps or the like, which is greatly higher than that of a conventional facsimile system using a public telephone network. When original data is simply encoded as in a conventional manner, processing can no longer be performed by software and requires large scale hardware.
With the conventional encoding method, encoded data may become larger in data amount than the original data depending upon the content of the original video data. In this case, the output rate of the video data from a scanner exceeds the encoding speed, and the reading operation of the scanner is intermittently performed. That is, the reading operation must be temporarily stopped so as to be restarted after completion of previous encoding.
Similarly, a fetching operation for fetching encoded data into a decoding circuit cannot follow a printer output, and the printer must be intermittently operated.